At seven months old, the Knoxville Zoo's first baby gorilla, Obi, is a petite, curious gymnast. Her bigger, slightly younger half-brother, Ubuntu, is the food-loving track star of the zoo's Gorilla Valley.

Both baby primates are proven crowd-pleasers; their summer births helped the zoo set record annual attendance in 2015. The park topped 430,000 visitors just before Christmas; officials expected the holidays to bring more visitors.

Many are likely to be looking for the inhabitants of Gorilla Valley. Obi and Ubuntu, along with their mothers and father, live in the natural habitat with a third adult female gorilla, Kowali. Another adult male gorilla, Wanto, lives alone in an adjacent habitat.

"Everybody who comes wants to see the babies," said Zoo President and CEO Lisa New. "They have their maps and they say, 'How do we get to the gorillas?"

It's common to see a crowd watching the gorilla family in their heated indoor courtyard, said zoo great apes keeper Leigh Rickey. Keepers have seen lots of new visitors, she said, along with frequent guests and zoo members.

Zoo staff members also are Gorilla Valley visitors. "We're all a little gorilla crazy right now," New said.

The ape infants aren't just fun to watch; they're a zoo milestone. They're the first of their endangered species born at the zoo. They're also the first Western lowland gorillas born in Tennessee in 30 years; those previous births were at the Memphis Zoo.

Gorilla Hope gave birth to daughter Obi May 28. Five days later Machi gave birth to son Ubuntu. Eighteen-year-old Bantu is the babies' father; they're his first offspring.

Zoo patrons gave the babies their names. Obi is West African for "heart;" Ubuntu is an African word meaning "I am because you are."

Both infants are curious, active and showing signs of their developing personalities. Ubuntu likes to dash about the courtyard "He's really fast and he likes to run. In the morning, he'll run in circles," Rickey said. "He's nonstop action as long as Machi is near. Then by dinner, he's crashed and is asleep."

Sometimes Ubuntu will pause and stand in a mini-gorilla stance, front hands resting on his baby knuckles and his back legs straight.

Obi toddles rather than strides like her brother. But she's a nimble climber. She often rides atop Hope's back, sometimes standing up as she travels. She seems easygoing. "She's in her own world," Rickey said.

The infants will continue to nurse their mothers for two to three years but are eating vegetables and other soft foods. Zoo visitors can quickly see the difference between the two. Ubuntu, with longer arms and legs, is larger. He also likes to eat and weighs five to six pounds. His thick hair seemed a deeper black than Obi's.

Petite like her mother and with red tints mixed with the black in her head hair, Obi could weigh four pounds. The youngsters' weights are estimates. Machi and Hope continue to carry their babies most of the time. Keepers haven't tried to take the babies to weigh them. As long as the infants continue to eat and thrive, it's unnecessary and much too stressful for baby and mother to attempt such checkups.

Both Hope, 32, and Machi 39, are experienced mothers. Each raised three other infants when they lived at other zoos. When Obi and Ubuntu walk on their own, they're never far from their mothers.

As they grow the babies play, chase and wrestle each other. On a recent December day, Ubuntu chased Obi in small circles about the courtyard as the adult gorillas snacked on bird seed. Sometimes Ubuntu caught Obi and rolled her on the ground. Other times Obi went looking for Ubuntu if he stopped running after her.

Both infants are curious about their 400-pound father Bantu. When one of his children approaches him, Bantu gently touches the baby or covers it with one of his massive hands. He doesn't get much one-on-one time, especially with Hope's Obi.

One recent day Obi three times wandered to her father. Within a minute each time Hope moved to Bantu and pulled their daughter from him. Hope's grown more protective of her daughter since an incident a couple of months ago, keepers say.

At that time Bantu was holding Obi but Hope didn't know it, Rickey said. When Hope discovered where her daughter was, she yelled at Bantu. The first-time father got upset and was uncertain how to respond. So he tossed Obi. The baby landed in a soft pile of hay. But since, Hope makes sure Obi doesn't go too far.

As Obi and Ubuntu grow, they'll play and climb more and exhibit some gorilla chest beating, Rickey said. And they'll likely grow up in Knoxville. Young captive gorillas often don't leave their families until they reach puberty.

Captive gorillas live into their 50s. A total of 341 gorillas live in zoos accredited by the Association of Zoos and Aquariums.